In the manufacturing process of the liquid crystal display, the polyimide (PI) solution needs to be coated onto the surface of a glass substrate, which is then dried through heating to evaporate the liquid solvent in the PI solution, leaving the solid components to form a layer of uniform film as the polyemid to make the liquid crystal molecules definite.
The common coating device with PI solution includes a heating plate, on which supporting legs are arranged for supporting the glass substrate on the heating plate which heats the air there above that then heats the glass substrate. A main problem of the device is as follows: with the supporting legs contacting the glass substrate and the heating plate at the same time, the temperature at the position in contact with the supporting legs on the glass substrate may be higher than where not in contact with the supporting legs, which results in a temperature difference and thus makes the solvent on the glass substrate evaporated at different speeds, thereby producing foot-like spots at the position corresponding to the supporting legs. There is still another problem as follows: after being coated with the PI solution, when the glass substrate is heated by the hot air between the glass substrate and the heating plate, the poor heat transfer property of gas may lead to a lower heating temperature, which makes both diffusion of the PI solution and the solvent evaporation slower, thus consuming more time. Furthermore, the airflow, due to non-visibility and instability, is very easy to make the temperature of the glass substrate non-uniform during the heat transfer process, and thus makes the solvent on the glass substrate evaporated and diffused at different speeds, thereby producing the cloud-like spots.